Add dragon support

Add runtime detection of dragon to fujinet-lib for coco.

Author: wdathing

coco/src/bus/bus_ready.c

@@ -11,6 +11,24 @@
 #include <dw.h>
 #include <fujinet-fuji-coco.h>
 
+
+#define DWWRT_VEC_DRG 0xD941
+#define DWREAD_VEC_DRG 0xD93F
+#define DWWRT_VEC_COCO 0xFA00
+#define DWREAD_VEC_COCO 0xF9FE
+
+static gbDWInited = false;
+// default to coco read/write if not inited.
+dwvec dwreadvec = DWREAD_VEC_COCO;
+dwvec dwwritevec = DWWRT_VEC_COCO;
+
+// detection logic for dragon stolen from: https://exileinparadise.com/tandy_color_computer:keyscn2
+//
+const uint16_t* RESET = 0xFFFE;       // Address of MPU Reset Vector
+const uint16_t VECCOCO = 0xA027;      // CoCo 1/2 reset vector value
+const uint16_t VECDRGN = 0xB3B4;      // Dragon32/64 reset vector value
+const uint16_t VECCOCO3 = 0x8C1B;     // CoCo3 reset vector value
+
 void bus_ready(void)
 {
     struct _readycmd
@@ -19,6 +37,16 @@ void bus_ready(void)
         uint8_t command;
     } rc;
 
+    if (!gbDWInited)
+    {
+        if (*RESET==VECDRGN)
+        {
+            dwreadvec = DWREAD_VEC_DRG;
+            dwwritevec = DWWRT_VEC_DRG;
+        }
+        gbDWInited = true;
+    }
+
     uint8_t z=0, r;
 
     rc.opcode = OP_FUJI;

coco/src/bus/dwread.c

@@ -6,8 +6,8 @@
  */
 
 #include <cmoc.h>
-
-typedef unsigned char byte;
+#include <coco.h>
+#include "dw.h"
 
 byte dwread(byte *s, int l)
 {
@@ -16,7 +16,7 @@ byte dwread(byte *s, int l)
         pshs x,y
         ldx :s
         ldy :l
-        jsr [0xD93F]
+        jsr [dwreadvec]
         puls y,x
         tfr cc,b
         lsrb

coco/src/bus/dwwrite.c

@@ -7,6 +7,8 @@
 
 #include <cmoc.h>
 #include <coco.h>
+#include "dw.h"
+
 
 byte dwwrite(byte *s, int l)
 {
@@ -15,7 +17,7 @@ byte dwwrite(byte *s, int l)
         pshs x,y
         ldx :s
         ldy :l
-        jsr [0xD941]
+        jsr [dwwritevec]
         tfr cc,d
         puls y,x
     }

coco/src/include/dw.h

@@ -10,6 +10,12 @@
 #define OP_FUJI 0xE2
 #define OP_NET 0xE3
 
+typedef unsigned char (*dwvec)(unsigned char);
+
+extern dwvec dwreadvec;
+extern dwvec dwwritevec;
+
+
 /**
  * @brief Read string to s from DriveWire with expected length l
  * @param s pointer to string buffer